Various types of systems have been used for controllably inflating and deflating vehicle tires during vehicle operation. Such systems typically include an air supply of pressurized air and controls for selectively increasing or decreasing an existing tire pressure, and for determining current tire pressures for each tire. The ability to selectively increase or decrease tire pressure is desirable in connection with optimizing the operation of the vehicle under widely changing conditions including weather, vehicular load, terrain, and vehicular speed.
A wheel valve tire air pressurization system is typically used for heavy vehicles having sets of tires pressurized thought respective manifolds and respective air channels. The wheel valve system has a wheel valve connected to each respective tire. The wheel valve is disposed in the air channel between an axle seal and the tires. The wheel valve can be shut off by air channel evacuation and thereby does not apply a continuous air pressure within the system through the axle seals leading to the tires. During the evacuation period when the wheel valve is shut off, the seal is not subject to air pressure. The lack of air pressure tends to extend the life of the axle air seal. The wheel valve system has one or more air manifolds each with a respective air channel connected to a respective set of wheel valves each set respectively connected to a set of tires. Each manifold controls the air flow through a respective channel which control a set of wheel valves and therefore controls the air pressure in a set of tires. Thus, a multiple manifold system can independently control multiple sets of tires, including for example, a set of front steering tires, a set of power drive tires, and a set of rear trailer tires. Each set of tires may have a respective desired tire pressure for a given traveling condition including speed, load and terrain. The use of multiple manifolds advantageously allows for simultaneous independent air pressurization adjustment of each set of tires. One programmed controller is used to control the tire pressure of the differing sets of tires. The wheel valve system has a cab mounted controller routing a cable of wires to each attached manifold.
One problem of prior system have included the inability to achieve inflation or deflation from one tire pressure to another with accuracy, and within a reasonable time period. It is desirable to provide a system which is efficient, minimizes operator involvement and obtains the required pressure accuracy within short inflating and deflating time periods. Complex flow control valves or valve orifice arrangements are not very effective to maintain and are undesirably expensive because small orifices tend to clog and are subjected to wear for reasons of high fluid velocities. Successful pressure monitoring systems are described in U.S. Pat. Nos. 4,782,878 and 5,309,969 both here incorporated by reference as there full set forth.
Prior art automatic control systems also suffer from a control problem called "hunting" when attempting to reach a desired set point tire pressure for a given operating condition. During a pressure inflation or deflation adjustment cycle, the system will either overshoot or undershoot the desired pressure generating wasteful repeated pressure adjustment cycles, before settling down to a stable pressure. Such systems produce long inflation and deflation times, inaccurate pressure adjustments and reduced reliability of operation. During an adjustment cycle, when dynamic pressure reaches the desired pressure, and the adjustment cycle is terminated, the air pressure may change to a stabilized static pressure which may not equal the desired pressure, which again, may cause the system to enter into another pressure adjustment cycle.
Prior systems also provide methods of eliminating hunting by shutting off the system in the dynamic closed loop operation with the use of pressure offset values to compensate for overshooting and undershooting and to provide a reduction in the inflation and deflation times. One problem associated with the prior system is the loss of pressure offset values when the system is turned off during vehicular parking. Another problem associated with the prior system are the errors in the offset corrections because the offset corrections do not compensate for the difference between the sensed pressures at the time of terminating the adjustment cycle and a subsequent stabilized static pressure. Yet another problem of the prior offset corrections is the use of constant offset values even during changing operating conditions which require changing offset correction values to maintain system performance.
Prior systems have also failed to address the need to conveniently change system operating functions and parameters especially useful during testing of experimental and newly designed vehicles and tires. Furthermore, air systems have been installed in a plurality of different vehicle models each having respectively desired operating functions and parameters disadvantageously requiring the manufacture of a respective plurality of unique systems or the manufacture of systems with dedicated additional, but unnecessary, model selecting switches. These and other disadvantages are solved or reduce using the present invention.